The following relates to printing systems. It finds particular application in conjunction with adjusting image quality in printing or marking systems with multiple electrophotographic or xerographic print engines. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Typically, in image rendering or printing systems, it is desirable that a rendered, or printed image closely match, or have similar aspects or characteristics to a desired target or input image. However, many factors, such as temperature, humidity, ink or toner age, and/or component wear, tend to move the output of a printing system away from the ideal or target output. For example, in xerographic marking engines, system component tolerances and drifts, as well as environmental disturbances, may tend to move an engine response curve (ERC) away from an ideal, desired or target engine response and toward an engine response that yields images that are lighter or darker than desired.
In the printing systems including multiple printing engines, the importance of engine response control or stabilization is amplified. Subtle changes that may be unnoticed in the output of a single marking engine can be highlighted in the output of a multi-engine image marking system. For example, the facing pages of an opened booklet printed by a multi-engine printing system can be printed by different print engines. For instance, the left-hand page in an open booklet may be printed by a first print engine while the right-hand page may be printed by a second print engine. The first print engine may be printing images in a manner slightly darker than the ideal and well within a single engine tolerance; while the second print engine may be printing images in a manner slightly lighter than the ideal and also within the single engine tolerance. While a user might not ever notice the subtle variations when reviewing the output of either engine alone, when the combined output is compiled and displayed adjacently, the variation in intensity from one print engine to another may become noticeable and be perceived as an issue of quality by a user.
One approach to improve print uniformity among multiple engines is for a user to periodically inspect the print quality. When inconsistency becomes noticeable, the user initiates printing of test patches on multiple engines and scans the test patches in. The scanner reads the test patches and adjusts the xerography of the engines so that lightness of a tone reproduction curve of one engine matches lightness of a tone reproduction curve of another engine. However, this approach requires a user intervention and the scanner to scan the test patches. Additionally, such approach does not improve contrast differences. Another approach to improve image consistency among multiple engines is to print test patches with the print engines, measure the test patches against one another, analyze the measurements and provide the system with a feedback of the analyzed data to adjust the xerography of the engines to match. However, such open loop feedback approach adjusts the printers with a time delay as such process is manual.
There is a need for methods and apparatuses that overcome the aforementioned problems and others.